1. Field of the Invention
The present invention relates to a liquid application device and an inkjet recording apparatus, and particularly to a liquid application device for applying liquid to a medium for a certain purpose which is, for example, to promote the coagulation of pigment when recording is carried out using an ink which contains the pigment as a coloring material. The present invention also relates particularly to an inkjet recording apparatus which includes a mechanism for applying liquid to a recording medium used in inkjet recording, for a purpose which is, for example, to promote the coagulation of pigment when recording is carried out using an ink containing the pigment as a coloring material.
2. Description of the Related Art
As modes of widely applying liquid or liquid material to a medium, spin coaters, roll coaters, bar coaters, and die coaters are known. These application modes are adopted on the assumption that the application is consecutively performed to a relatively long application medium. As a result, when application media with a relatively small size are intermittently fed, and the application is performed to these media, the problem can occur that a uniform coating film cannot be obtained due to the irregularities of beads of coating material at the start or the end point of the application, for example.
As a configuration capable of solving such a problem, one which is described in Japanese Patent Application Laid-open No. 2001-070858 is known. This is a die-coater type, in which a rotating rod bar is used, and coating material is discharged from a discharging slit to the rod bar to form a coating film on the rod bar. The formed coating film is brought into contact with an application medium and is transferred thereto as the rod bar rotates. When the coating film formed on the rod bar is not transferred or applied to an application medium, the coating material returns into the head as the rod bar rotates, and the material is collected via a collection slit. In other words, even when the application is not carried out, the rod bar keeps rotating, and the coating material remains forming a coating film on the rod bar. In this way, it is made possible to obtain a uniform coating film even when the application media are intermittently supplied, and the application is intermittently performed thereto.
Among inkjet recording apparatuses, one which utilizes a liquid application mechanism is known. According to the description in Japanese Patent Application Laid-open No. 2002-517341, a doctor blade abutting a roller is used, coating liquid is stored between the blade and the roller, and the coating liquid is applied to the roller as the roller rotates. As the roller rotates, the applied coating liquid is transferred or applied to a base material transferred between this roller and another roller. Also in Japanese Patent Application Laid-open No. 8-072227 (1996), shown is a mechanism which previously applies a treatment liquid insolubilizing dyes before recording, in an inkjet recording apparatus. The description of the first example in this document discloses that the treatment liquid in a replenishing tank adheres to a rotating roller and is thus pumped, and, at the same time, the pumped treatment liquid is applied to a recording paper.
However, with regard to the configurations described in the above documents, Japanese Patent Application Laid-open No. 2001-70858, Japanese Patent Application Laid-open No. 2002-517341 and Japanese Patent Application Laid-open No. 8-72227 (1996), the rod bar or the roller rotates, and the application liquid is applied or supplied to the surface of the bar or the roller, in which the area where the application or supply is performed, is opened to or communicates with the atmosphere. For this reason, there arises the problem of vaporization of the application liquid. In addition, there is a possibility that the problem can occur that, when the position of the apparatus changes, this results in the leakage of the application liquid.
Among others, with regard to the inkjet recording apparatuses, such as printers, with the leakage of the liquid due to the position change at the time of carrying taken into consideration, it is difficult to apply the application mechanism described in the above documents to downsized apparatuses.
Meanwhile, in Japanese Patent Application Laid-open No. 8-058069 (1996), disclosed is a gravure printing machine having a configuration in which the area is sealed off where ink as the application liquid is applied or supplied to a roller which has a print pattern formed on the surface thereof. With regard to this apparatus, an ink chamber having two doctor blades is brought into contact with the circumferential surface of the roller to form a liquid room (an ink reservoir) between the chamber and the roller.
In the apparatus described in Japanese Patent Application Laid-open No. 8-58069 (1996), a pump is provided between an ink tank to store ink and the liquid room. The ink in the ink tank is pumped into the liquid room by the pump, so that the ink is supplied from the ink tank to the liquid room. In addition, the ink in the liquid room is sent to a receiving tank which receives the ink discharged from the liquid room.
In that occasion, in a case where the apparatus has been stopped for a long time period, thickening or sticking of the application liquid due to vaporization and precipitation thereof sometimes occurs in the ink room and in a flow channel for sending ink to the ink room. However, with respect to this problem of thickening and sticking of the application liquid in the flow channel, there is no mention in Japanese Patent Application Laid-open No. H08-58069 A.
In a case where the application liquid has vaporized in the channel and thereby has thickened or stuck therein, circulation of the application liquid is sometimes hindered. As a result it is sometimes made difficult to perform favorable circulation to the extent that reliability of the application device can be maintained. For example, when the thickening has occurred in the ink room, viscosity of the liquid to be applied has become higher than usual. In a case where an adequate application has been hindered thereby, partial nonuniformity in the application is sometimes generated. There is concern that this nonuniformity adversely affects the image to be printed eventually such as mottling.